Colour, Grayscale or Black and White: Choosing the Right Scan Mode
What each scan mode does, which documents suit which mode, and how the choice affects readability and file size.
Most scanning apps offer several ways to process a page: original colour, grayscale, and high-contrast black and white. Choosing well makes documents look sharper and files smaller.
The main modes
Colour (original). Keeps all the colours of the page. Best for anything where colour carries meaning: logos, stamps, photos, highlighted text, charts and coloured forms.
Grayscale. Converts colours to shades of grey. Good for pages with shading, pencil notes or photos where you don't need colour, and often produces smaller files than colour.
Black and white (high contrast). Turns everything into pure black or white. Ideal for plain text pages, printed forms and typed letters. Makes the paper background white and text dark, and creates the smallest files.
Which mode for which document?
| Document | Suggested mode |
|---|---|
| Typed letters, contracts, forms | Black and white |
| Handwritten notes in pen | Black and white or grayscale |
| Pencil notes | Grayscale |
| ID cards, certificates, stamps | Colour |
| Documents with photos or charts | Colour |
| Whiteboards | Colour or high contrast |
| Receipts | Black and white or grayscale |
| Old photographs | Colour |
Effect on file size
Colour scans hold the most information, and so are the largest. Black and white scans are usually a fraction of the size. For a 20-page contract, choosing black and white can make the difference between an attachment that goes through and one that's rejected for size.
Effect on readability
Black and white can make text very crisp, but may drop faint details, such as light pencil, pale stamps or thin lines. Grayscale keeps subtle tones. If you're unsure, scan a page in two modes and compare.
Keep colour when it matters
Some official documents rely on colour for authenticity, such as coloured seals or security backgrounds. If a portal specifies colour, don't convert.
Mixed documents
A single document with text and photos might need colour for a few pages and black and white for the rest. Scan in the mode that suits each page, but keep them in one PDF when the app allows.
Check the enhancement
High-contrast modes can turn a yellowish page white, or, with poor lighting, can turn parts of the page black. Inspect the result, and re-scan with better lighting if needed.
Printing
If you plan to print, consider the printer's colour capabilities. Black and white scans print quickly and use less ink.
Rule of thumb
Use colour when colour carries information, black and white for plain text, and grayscale in between.
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